1. Field of the Invention
The present invention relates to a pulse wave radar device which uses a millimetric wave or a submillimetric wave. More specifically, it relates to a pulse wave radar device which reduces mistakes in decision owing to a noise.
2. Description of the Related Art
A pulse wave radar device is used which sends a pulse-modulated transmitting pulse wave and receives a receiving pulse wave reflected from a target, to calculate a distance to this target. Since a round-trip distance to a target can be obtained by integrating the light velocity with a lapse of time from a moment of sending transmitting pulse waves to a moment of receiving reflected waves from the target, the pulse wave radar device measures a lapse of time from a moment of sending a transmitting pulse to a moment of receiving a reflected wave from a target, to calculate a distance to the target.
In the pulse wave radar device, in detection of receiving pulse waves that are reflected from the target and come back to the pulse wave radar device, a threshold value is established so that a pulse larger than the threshold value may be decided to be a receiving pulse. If the threshold value is established high, noise resistance is improved but a faint pulse from a long distance cannot be detected. If the threshold value is established low, on the other hand, a faint receiving pulse from a long distance can be detected but a noise contained in a received signal may possibly be detected as a receiving pulse. In the received signal, a lot of components are mixed such as a noise from a switching regulator used for a power source, a noise from an electric product, and a pulse transmission wave from other pulse wave radar devices.
A pulse wave radar device is disclosed which decides such a component to be a noise if its magnitude is larger than a theoretical maximum receiving intensity (see Japanese Patent Application Laid-open No. 2003-302462 for example). In this device, a maximum possible receiving pulse from the target is computed for each distance to the target so that a receiving pulse larger than this maximum possible receiving pulse from the target may be decided to be a noise.